In 2016, soldiers of the 7th Division of the Nigerian Army prepare to leave Maiduguri in a heavily armed convoy on the road to Damboa in Borno State, where at least six soldiers died in separate Boko Haram attacks in December 2017 (AFP Photo/STEFAN H

Military authorities say Nigerian soldiers have arrested more than 400 people associated with the Boko Haram extremist group hiding on the islands of Lake Chad, including fighters, wives and children.

The two-week operation netted the largest number of arrests of Boko Haram fighters in recent months in northeast Nigeria, Col. Onyema Nwachukwu said. The operation included air and ground offensives.

The military said many Boko Haram insurgents were killed, but it did not give details.

Among those arrested were 167 Boko Haram fighters, 67 women and 173 children. The women and children will be handed over to authorities of displacement camps after investigations, the military said.

Another 57 insurgents were arrested during a separate operation in another part of the troubled region.

Boko Haram has been blamed for more than 20,000 deaths during its eight-year insurgency, which has spilled over into neighboring countries and created a vast humanitarian crisis with millions displaced and hungry.

Human rights groups have expressed concern about the large number of women and children who have been arrested in the fight against Boko Haram, saying most of those detained have been picked up at random and without reasonable suspicion.

In an effort relieve overcrowded military detention facilities, Nigeria's government in October began the trials of more than 1,600 suspected Boko Haram members behind closed doors at a military barracks. It was the largest mass trial in the Islamic extremist group's history.

While Nigeria's president late last year declared the extremist group had been "crushed," leader Abubakar Shekau remains elusive and the group in recent months has carried out a growing number of deadly suicide bombings and other attacks. Many have been carried out by women or children who were abducted and indoctrinated.

Earlier this week, dozens of Nigerian state governors approved the transfer of $1 billion to aid the federal government's fight against Boko Haram, signaling that the announcements of victory over the extremists had come too soon.